Yeah, the quests are good and there's some really intriguing and philosophical lore (but if you're lazy you could even look it up on the wiki). Btw Naganadel is not that cheap. Utraboost is good but to be fair it's a 540 stat mon and i'm under the impression that as of episode 19 he will be not even remotely broken. Your choice. Then you will need to look for z-crystals, megastones (there are some that surprised me being in the game while other are actually not in yet) and some tms (good luck on getting Thunderbolt).
I mean, there's so much in this game I enjoy exploring it. But on the competitive side you're done. No good battles anymore. But you can always rerun with some restrictions. There are different paths in this game for a reason.